Conventionally, power saving has been an important technical issue, especially for battery-powered portable personal computers, PDAS, and other data processing devices, to extend the battery operation time. Some power saving method not only reduces static power consumption during operation but also dynamically minimizes power consumption depending upon operation states.
Japanese Patent Laid-Open Publication No. Hei 7-261889 discloses a system that has a pseudo device driver installed for power saving operations. The system periodically checks the last access time of each power-manageable hardware component in the computer system. Upon detecting a hardware component being in an idle state, the system orders the device driver corresponding to the idle-state hardware component to reduce power to be supplied to the idle-state hardware component.
Japanese Patent Laid-Open Publication No. Hei 9-101847 discloses a computer system that switches the CPU operation mode to a power saving mode when the event queue in the operating system does not contain any event. In the power saving mode, the system stops the CPU operation clock or stops the oscillator.
The prior art disclosed in the Japanese Patent Laid-Open Publication No. Hei 7-261889 described above takes time to detect an idle state. On the other hand, the prior art disclosed in Japanese Patent Laid-Open Publication No. Hei 9-101847 described above quickly detects an idle state.
However both prior-art systems provide general power saving modes, and there is yet room for improvement in flexible power saving.
In view of the foregoing, it is an object of the present invention to provide a power saving method and a power saving unit that dynamically select a more appropriate power saving mode depending upon operation states of the computer system.